Function potentiometer



Nov. 25, 1958 R. K. BONELL 2,862,086

FUNCTION POTENTIOMETER Filed March 5, 1956 2 Sheets-Sheet 1 INVENTOR Nov. 25, 1958 v Filed March 5, 1956 R. K. BONELL 2,862,086

FUNCTION POTENTIOMETER 2 Sheets-Sheet 2 l mmlm-inml Fig.4

E & d 3 (9 0 360 DEGRESS SHAFT DISPLACEMEMENT' Fig.9

F 6 INVENTOR FM W 2,862,086 Patented Nov. 2 5, 1958 FUNCTION POTENTIOMETER Ralph K. Bonell, Stratford, Pa. Application March 5, 1956, Serial No. 569,634

Claims. (Cl. 201-48)" This invention relates to potentiometers, rheostats and the like and it refers more particularly to devices of the above character designed to supply an electrical output that is a selected function of an input displacement or position.

Prior art potentiometers, for'example those furnishing an output voltage that is a non-linear function of the position of the movable contact thereof and hence of the shaft mounting the contact assembly, commonly have been constructed by winding resistance wire on a cardf formed in accordance with the selected relationship of shaft position and output voltage. It is diflicult to design a card and to wind it in the manner necessary to produce the exact functional relationship desired and, once wound, it is not possible to change the established relationship.

Thepresent invention overcomes these disadvantages ofearlier function potentiometers and like devices by providing a cam-controlled potentiometer assembly comprising in novel combination a linear potentiometer element and a cam mechanism whereby a desired function of input shaft position may be reproduced as anoutput voltage by forming the contourofthe caminaccordan ce,

with a polar plot of the function. The use of a true polar plot, which is simple to calculate and construct, is made possible by guiding the cam follower along a line passing through the center of the base circle of the cam, that is, through the center of the shaft mounting the cam. Minorcorrections to the lift of thecam can readily be made and a change'of cams accomplished without disturbing the po-tentiomete'r'elem'ent, proper. This is a considerable advantage, for example in experimental work, in arriving at a favorable relationship between an independent and a dependent variable. The assembly forms a compact, readily mounted unitary structure which may be employed in a variety of ways as an element of servo systems, analog computers, test apparatus, etc.

It is an object of the invention to provide a function potentiometer or like device adapted to displace contact means along a resistance winding in desired functional relationship to the displacement of input driving means.

Another object is to provide a function potentiometer wherein the relationship of mechanical input and electrical output may readily be varied without modification of the resistance member of the device.

Another object is to provide a unitary structure for performing the foregoing functions which is readily mounted on support means and the operating members ofwhich are readily accessible for replacement and adjustment.

Other objects and advantages will appear herein.

-In the drawings:

Fig. l is a top plan view, partly in section, of a potentiometer constructed in accordance with the principles of the invention;

Fig. 2 is a view similar to Fig. 1 with certain members omitted, more clearly to show other members;

Fig. 3 is a section along the line 33 of Fig. 1;

United States Patent Ofiice Fig. 4 is a section along the line 4-4 of Fig. 1;

Fig. 5 is a bottom plan view of the potentiometer of Fig. 1, to a reduced scale;

Fig. 6 is a view of a cam blank, with markings illustrating the manner of laying out a cam contour;

Fig. 7 is a section along the line 77 of Fig. 5;

Fig. 8 is a wiring diagram;

Fig. 9 is a graphical diagram, for purposes of explanation; and

Fig. 10 is another wiring diagram.

In the figures, potentiometer assembly 11 comprises a cylindrical shell 13 removably mounting end plates 15 and 17 to form a substantially closed housing. The frame or supporting structure of the device is completed by intermediate plate 19 spaced from plate 17 by studs 21. Input shaft 23 is journaled in bushing 25 secured to plate 17 by nut 27 and in bushing 29 secured to plate 19 by nut 31. Cam assembly 33 comprises a cam locking plate 35 and a cam assembly mounting plate 37 removably mounted on shaft 23 by set screw 41. Between these two plates cam 43'is held in an angular position determined by pins 45 fast in plate 37 and projecting through the cam into plate 35. Plates 35 and 37 are clamped by screws 47. A cam follower 49 bears against the periphery of cam 43 and is rotatably mounted by stud 51 on slide plate 53, forming a part of the cam follower assembly. Plate 53 is guided for translation along a line passing through the center of shaft 23 by grooved rollers 57 rotatably mounted on plate 19. Plate 53 has an elongated apertureSS accommodating shaft 23.

On the edge ofplate 53 a toothed rack 59 is cut which is engaged by pinion 61 fast on shaft 63. This shaft is journaledfin bushings 65 and 67, the former held-in plate 19 andthe latter secured to plate 17 by nut 69. Adjacent bushing 65 shaft 63 mounts grooved pulley 71 about the periphery of which cord 73 having one end fast on the pulley is wrapped and unwrapped as the shaft rotates. At the end opposite the pulley cord 73 is attached to spring 75 anchored on stud 77 mounted on plate 19, thereby to supply a force tending to rotate shaft 63 and through the medium of-members 61, 59 and 53 to keep follower 49 in contact with the periphery. of cam 43.

A flanged hub 79 mounted on shaft 63 adjacent pulley 71 and secured by set screw 81 carries a bent radiallyextending contact arm 83 which bears, at the outer contact-making portion thereof on resistance winding 85 of the potentiometer element, proper. Resistance member 85 is formed to an arc of a circle concentric with the axis of shaft 63 and is mounted on disc member 87 of insulating material rotatable about shaft 63 for zero adjustment or other purposes requiring relative displacement of arm 83 and winding 85 independently of rotation of shaft 23 or 63. This adjustment is provided by bracket 89 mounted on disc 87 which has a threaded hole engaged by screw 91. Spring 93 constrained by collar 95 on screw 91 and bracket 97 on shell 13 provides a resilient bias for the adjustment. External connections to winding 85 and contact arm 83 are made by way of insulated terminal posts 161, 163 and 165 (Fig. 5), assuming plate 17 to be of metal.

A blank 43 for a cam 43 is shown in Fig. 6. This flat plate may be of metal, plastic or other suitable substance. Cams for experimental use will be formed from easily worked material while the material for permanent cams will usually be a metal. Blank 43 is provided with a central hole 107 to accommodate shaft 23 and with holes 109 and 111 for screws 47 and pins 45, respectively. In laying out a desired cam contour a base circle 113 concentric with hole 107 and radial lines 115 are inscribed on the blank, or they may be permanently imprinted thereon. Points 117 on the desired cont-our are plotted radially from circle 113, as from point 119 thereon, and connected with a smooth curve. Since the line of displacement of slide 53 passes through the center of shaft 23 this curve can be calcnlated and constructed as the truepolar plot of the desired function about the axis of this shaft, if the radius of follower 49 is of negligible significance as will usually be the case with permissible pressure angles. A correction for the radius'of the follower, if necessary, can be made according to known cam design theory.

Fig. 8 illustrates one circuit connection for the electrical elements of the potentiometer of Fig. 1. A source of potential, exemplified by battery 121, is connected across winding 85 and the output taken at terminals 101 and 103. This allows an output voltage excursion corresponding to full battery voltage without reversal of sign. Where a reversal of sign is desired a center-tapped source connected according to Fig. may be employed. In Fig. 9 which shows an assumed curve of potentiometer output voltage the left-hand scale of ordinates applies in the case of the connection of Fig. 8 while the right-hand scale applies to that of Fig. 10.

There has been disclosed herein means for deriving an electrical quantity that is a selected function of a mechanical displacement or of position. While potentiometers are principally referred to in the specification and claims and illustrated in the drawings, the construction of rheostats and like devices in accordance with the principles of the invention fall within the scope of the invention as will be apparent to persons skilled in the art.

What is claimed is:

l. In a function potentiometer the combination of a frame, first and second shafts journaled thereon in spaced parallel relationship, a cam mounted on said first shaft, follower means for said cam, means mounting said follower means on said frame for guided displacement relative thereto along an axis normal to and intersecting the axis of said first shaft, means for rotating said second shaft in proportion to the displacement of said follower means along said axis, a circularly formed resistance element mounted on said frame concentric with said second shaft, contact means mounted for rotation with said second shaft cooperative with said element to make contact therewith at various points therealong, and terminal means for making connections to said element and contact means, respectively.

2 In function potentiometers and the like the combination of a frame, a shaft journaled thereon for continuous rotation, a fiat cam having the periphery thereof contoured with respect to a'base circle in accordance with a polar plot of a function of shaft position to be derived in electrical form, means removably mounting said cam on said shaft including a plate adjustably mounted on said shaft adapted to receive said cam in surface contact relation and having means defining a unique mounted position of the cam relative thereto and establishing a concentric relationship of said base circle and shaft, a circular resistance winding mounted on said frame, contact means displaceable therealong, and means actuated by said cam and operable throughout complete rotation of said shaft for setting the position of said contact means in accordance with the contour of said cam.

3. The combination defined in claim 2 wherein means are provided for efiecting a relative displacement of said winding and contact means independently of displacement of said shaft.

4. In function potentiometers and the like the combination of a frame, f rst and second shafts journaled thereon in spaced parallel relationship, a cam, means removably mounting said cam on said first shaft in fixed relationship relative thereto, a resistance element mounted on said frame for limited displacement relative thereto, a contact displaceable therealong, displacing means therefor including follower means forsaid cam supported on said frame for displacement along a line normal to and intersecting said first shaft, a toothed rack borne thereby having the axis thereof parallel to said line, a pinion mounted on said second shaft meshing with said rack and an operative connection between said pinion and contact, and means for displacing'said resistance element relative to said frame to effect displacement thereof relative to said contact independently of rotation of either of said shafts.

5. The combination defined in claim 1 wherein means are provided for effecting a relative displacement of said resistance element and said contact means independently of displacement of said first shaft.

References Cited in the file of this patent UNITED STATES PATENTS 629,039 Luitwieler July 18, 1899 1,050,226 Nixon Jan. 14, 1913 1,971,238 Silling Aug. 21, 1934 2,561,140 Schaefer July 17, 1951 

